# What physical property is identical for the isomers of C_5H_12 and C_6H_14?

$\text{Pentane}$, ${C}_{5} {H}_{12}$, can form THREE structural isomers: $\text{isopentane}$; $\text{n-pentane}$; and $\text{neopentane}$.
$\text{Butane}$, ${C}_{4} {H}_{10}$, can form TWO structural isomers: $\text{isobutane}$; $\text{n-butane}$.
For each isomeric series, while they have (slightly) different chemistries, and physical properties. THE MOLECULAR MASSES, $58.12 \cdot g \cdot m o {l}^{-} 1$, and $72.15 \cdot g \cdot m o {l}^{-} 1$, respectively, ARE A CONSTANT...